Low vitamin D status associated with cognitive decline: Study

Inadequate dietary intake of vitamin D is associated with higher levels of cognitive impairment; however it remains unclear if the link is causal, according to a new study.

The study, published in Neurology​, suggests that a weekly intake of less than 35 micrograms of vitamin D is associated with a greater incidence of cognitive impairment. However the researchers noted that the association could be causal in either direction, stating it is possible that low vitamin D is a result of, rather than the cause of cognitive impairment.

“The main finding of this population based study …was that the weekly dietary intake of vitamin D was significantly associated with the global cognitive performance in both linear and logistic regression models, even while considering the effects of all potential confounders,”​ said the researchers, led by Dr Cédric Annweiler from Angers University Hospital, France.

D and cognitive decline ​

Cognitive performance declines naturally as we age, but it has been suggested that vitamin D status could impact on cognitive function among older adults.

It is suggested that vitamin D binds to neuronal receptors in the brain, and develops an anti-neurodegenerative action through, anti-inflammatory and antioxidative. Many people have therefore recommended that maintaining an adequate vitamin D status is essential to avoid vitamin D deficiency– induced cognitive decline.

Data from David Llewellyn and colleagues at the University of Exeter, England, indicated that insufficient levels of vitamin D may accelerate cognitive decline​. The scientists analyzed vitamin D levels from blood samples of 858 adults and found that severe vitamin D deficiency was associated with a 60 percent increase in the risk of substantial cognitive decline.

Annweiler and colleagues said the benefits of vitamin D intake in treating or preventing cognitive impairment remain unknown, adding that, to date no randomized controlled trials have explored the benefits of vitamin D supplementation to treat or prevent cognitive impairment.

But, before conducting such a trial, they said it would be of benefit to determine whether dietary, non-supplemented, intake of vitamin D could be associated with cognitive performance in older adults.

“We had the opportunity to examine the association between dietary intakes of vitamin D and global cognitive performance in a large representative community survey of older women,” ​said the researchers.

Study details​

A total of 5,596 women, not taking vitamin D supplements were divided into 2 groups according to their baseline weekly staus: either inadequate (less than 35 micrograms per week) or recommended (more than 35 micrograms per week).

Compared to women with recommended weekly vitamin D dietary intakes, women with inadequate intakes were reported to have lower scores on the SPMSQ mental state questionnaire.

The researchers observed that inadequate intakes were more often associated with cognitive impairment, as defined by an SPMSQ score of less than 8.

“We found an association between weekly vitamin D dietary intake and SPMSQ score. Inadequate weekly vitamin D dietary intakes were also associated with cognitive impairment,”​ wrote the researchers.

Causation​

Exactly how low dietary intakes of vitamin D and decreased cognitive performance are associated remains unclear. Annweiler and co workers noted that it is yet to be clarified whether the of association is causal, and if so, in what direction the causation may be.

They stated that it remains a possibility that low vitamin D status may be a result of poor diet, due to cognitive decline. But, emphasized that vitamin D insufficiency has been suggested as a contributing factor to hypertension, which itself is a major risk factor in the development of cerebrovascular diseases and cognitive decline.

Annweiler and colleagues added that nutrients are not consumed in isolation, “but rather as components of an overall diet, which is precisely considered as a modifiable risk factor for cognitive decline.”​

Moreover, they said that as a component of diet, low vitamin D intake may be a surrogate measure for other nutritional abnormalities, which in turn may lead to cognitive decline.